OXYGEN ION ACCELERATION AND CONVECTION IN THE POLAR MAGNETOSPHERE B. Klecker for the CLUSTER Team at...
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OXYGEN ION ACCELERATION AND CONVECTION IN THE POLAR MAGNETOSPHERE
B. Klecker
for the CLUSTER Team at MPE
G. Paschmann, B. Klecker, M. Förster, H. Vaith, J. Bogdanova, E. Georgescu, S. Haaland, P. Puhl-Quinn
A. Blagau, A. Kis,H. Hasegawa, B. Sonnerup
Presentation at the Fachbeirat MPE 2002June 17 - 20, 2002
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OUTLINE
• The CLUSTER Mission and Payload
• The Experiments EDI and CIS
• Ion Convection Measurements: a Tool
– to study spatial and temporal variations
– to study wave signatures
– to derive spatial scales from time series measurements
• Summary
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CLUSTER: CORNERSTONE #1 (WITH SOHO) OF ESA‘S SCIENTIFIC PROGRAM AND PART OF ISTP
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CLUSTER ORBIT IN FEBRUARY 2001
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CLUSTER SEPARATION STRATEGY
Year Mission Phase Sep. (Km)
2001 nominal Cusp 600
2001 nominal Tail 2000
2002 Nominal Cusp 100
2002 Nominal Tail 3810
2003 Extended Cusp 5000
2003 Extended Tail 100-700
2004 Extended Cusp 100-700
2004 Extended Tail 10000
2005 Extended Cusp 10000-20000
2005 Extended Tail 20000
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CLUSTER INSTRUMENTATION
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CLUSTER OPERATION
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THE ELECTRON DRIFT INSTRUMENT (EDI)
Scientific Objectives
Measurement of the ambient electric field by a novel technique developed over the last 20 years:
Emission and subsequent detection of tracer electrons by two sets of electron gun / detector units, positioned at 180° to each other.
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THE ELECTRON DRIFT INSTRUMENT (EDI)
For any combination of magnetic field B and drift velocity V, only a single electron trajectory exists that connects each electron gun with the detector located on the opposite side of the S/C.
Technique:
Emission of an electron beam of 1 keV perpendicular to the local magnetic field.
Detection of the electrons with the detector on the opposite side of the S/C.
Measurement of the times-of-flight, T1 T2.
Computation of E from the drift step d, and B
d = Vd Tg ~ E / B2
T1,2 = Tg (1±Vd/Ve)
T1-T2 = 2 (d/Ve)
T1+T2 = 2 Tg = 4 me / e B
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EDI: Triangulation and Time-of-Flight Technique
Triangulation Technique
By employing 2 beams and 2 detectors, the two unique directions can be monitored continuously and the displacement d obtained by a triangulation procedure.
Time-of-Flight Technique
When the magnetic field B becomes small, d ~ E/B2 becomes very large and cannot be determined accurately any more with the triangulation technique. Then d can be determined with higher precision from the time-of-flight differences.
T1-T2 = 2 (d/Ve)
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EDI DATA PRODUCTS
• Electric field time series
• Vtime series
Time resolution: ≥100 msec, standard 1 sec
Limitations: magnetic field strength, typically B > 15 nTrapid time variations in E or Bsignal to background ratiodata from S/C-1, S/C-2, S/C-3
Note: EDI provides V without any additional assumptions
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THE CLUSTER ION SPECTROMETRY INSTRUMENT (CIS)
Scientific Objectives / Instrument Requirements
Determination of the 3D Distribution function of ions in the energy range
~ 0 (S/C-potential) to 40 keV/e with 1 spin (4 sec) time resolution.
Identification of major ions in the near-Earth plasma environment, i.e. of H+, He2+, He+, and O+.
Technical solution to cover large dynamic range and to provide
redundancy: 2 sensors with 2 geometry factors each (factor ~100 )
CIS-1 (CODIF) Composition and Distribution Function Analyzer
On-board analysis provides H+, He2+, He+, and O+.
Ground analysis provides in addition O2+ and O2+
Energy range 0.020 - 40 keV/e + ~ 0 (S/C-potential) - 20 eV with RPA
CIS-2 (HIA) Hot Ion Analyzer
Ion energy range 0.005 - 32 keV/e
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CIS-1: Principle of Operation
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CIS DATA PRODUCTS
ON-BOARD ANALYSIS
• Moments (N, V, T, P) computed onboard every spin (4 sec) from 3D distributions for H+, He2+, He+, O+
• 3D Distributions of H+, He2+, He+, O+ for ≥ 1 spin -> telemetry
ANALYSIS ON GROUND
• 3D Distributions of H+, He2+, He+, O+ with max. 1 spin resolution.
• Moments (N, V, T, P) computed for selectable energy ranges.
Limitations: Counting statistics
Data from S/C-1, S/C-3, S/C-4
Plasma Drift / Convection: V derived from V and magnetic field B
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PLASMA CONVECTION MEASUREMENTS
Measurements with the 4 CLUSTER S/C provide a tool for
the study of
• Spatial and temporal variations
• Spatial scales
• Wave signatures
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OBSERVATIONS IN THE DAYSIDE POLAR CAP
SUN
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• The velocity distribution of O+ shows a mono-energetic beam with systematic time dispersion.
• For Bz < 0 the energy is systematically decreasing with increasing latitude.
• The convection velocity inferred from the O+ velocity measurement and V as measured directly with EDI are in remarkably good agreement.
• The pole-ward convection is consistent with the 2-cell convection patterns as typically observed in the ionosphere for Bz < 0 .
Typical Signatures of O+ Beams in the CUSP and Polar Cap
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Oxygen Beams in the Cusp and Polar Cap
Interpretation
Localized (in latitude) source of accelerated ionospheric ions with broad energy spectrum.
Velocity, V, from super-position of outward particle motion (VII) with pole-ward
convection (V)
This results in an apparently mono-energetic beam as observed on CLUSTER
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MULTISPACERAFT OBSERVATIONSCLUSTER CONFIGURATION ON MARCH 4, 2001
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MULTISPACECRAFT MEASUREMENTS
a) Energy-time spectrogram of O+.
b) Number density of O+ on S/C 1, 3, 4.
c) V|| of O+ on S/C 1, 3, 4.
d) V of O+ on S/C 1, 3, 4.
Note:
• For separation distances of ~ 600 km the convection velocities are essentially identical on all 3 S/C.
Check for time-lag between different S/C provides length-scale of coherence of convection.
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CROSS - CORRELATION: CIS
CIS S/C-3 - S/C-4
Cross-correlation of V as
measured with CIS with 16 s resolution. Maximum correlation is obtained for zero time lag.
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CROSS - CORRELATION: EDI
Cross-correlation of V as
measured with EDI with 1 s resolution. Maximum correlation is obtained for zero time lag.
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SUMMARY-1
• The convection velocities derived from the O+ moments are in remarkable agreement with the drift velocity measured directly with the EDI experiment onboard CLUSTER. Thus, the combination of CIS and EDI measurements provide a full set of 4 S/C measurements with redundancy (2 x S/C-1, S/C-2, 2 x S/C-3, S/C-4)
• For separation distances of ~ 600 km the convection velocities are essentially identical on all spacecraft. This implies that the observed variations in V are temporal in nature, i.e. due to changes in the
convection pattern probably caused by substorm related activity.
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Energy step structures of O+ and H+ ions in the cusp and polar capO+ distribution functions, S/C 1
• At 02:25:20 the O+ distribution function shows a beam-like behavior, at 02:35:40 the distribution function shows high perpendicular heating.
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NEXT STEPS
Convected O+ Ions
• Correlate variations in convection velocity with substorm activity.
• Compare the O+ energy dispersion with model calculations (trajectory tracing). This method can be used, together with the information on the convection velocity, to infer the altitude distribution of ion injection and acceleration (e.g. Dubouloz et al., 2001, Bouhram et al., 2002).
• Use the multi-spacecraft measurements to infer the latitude and longitude distribution of ion injection (for larger separation distances).
Perpendicular Heating
• Detailed correlation with wave measurements onboard Cluster
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CONVERSION OF TIME SERIES DATA INTO SPATIAL PROFILES AT THE MAGNETOPAUSE
• The 4 MP crossings provide the magnetopause orientation and velocity at discrete instances in time.
• Continuous sensing of the magnetopause velocity is possible with the measurement of the plasma drift velocity made with EDI and CIS. Panel 3: VN, the drift velocity along the MP normal (EDI and CIS).
• Integration of VN defines the distance from the MP to the S/C (Panel 4).
• This distance scale can then be used to convert the time series data into a spatial profile.
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STANDIG ULF WAVES IN THE POLAR REGION
• Phase shift between B and V = 90°
STANDING WAVE
• Positive Pointing Flux
Energy Input into Ionosphere
SUN
C1,C2,C4C3
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C4
C1
C3
C1
C3
C2
C4
From OVT 16 UT Tsy87, KP=3
XGSM
ZGSM
Ion
Ion
Ion
UT 15:00 15:30 16:00 16:30 17:00 17:30 18:00ILAT 66.20 73.00 79.90 85.80 89.50 86.30 83.70MLT 12.40 12.50 12.70 12.90 23.40 00.40 00.80
UT 15:00 15:30 16:00 16:30 17:00 17:30 18:00ILAT 66.80 72.70 78.80 84.30 88.80 88.10 85.10MLT 12.40 12.50 12.60 12.70 12.80 00.90 00.90
UT 15:00 15:30 16:00 16:30 17:00 17:30 18:00ILAT 61.80 64.90 70.70 77.40 83.50 88.40 87.70MLT 12.20 12.30 12.40 12.40 12.30 11.00 01.80
CUSTER-CIS Day 30 - 08 - 2001
STUDY OF TIME VARIATIONS
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Cluster C3
Ion
15:00 15:30 16:00 16:30 17:00 17:30 18:00Time UT (HH:MM)
IMF
SuperDarn
C3
Geotail + 10mn
VcCIS
12
MHD
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Cluster C3
Ion
15:00 15:30 16:00 16:30 17:00 17:30 18:00Time UT (HH:MM)
IMF Geotail + 10min
SuperDarn MHD
C3 12
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Summary-2
• Double cusp observed when IMF turned from South to North and dominant IMF-By negative.
• Second cusp observed on CLUSTER-3 is the cusp for Bz>0 that moved poleward.
• CIS and EDI measurements of plasma convection in the polar region can be used to investigate in detail changes of the convection pattern in response to solar wind conditions.
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C3 C4,C2,C1
Start of cusp at C4,C2,C1SuperDarnMHD simulation
C4
12 12
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Cluster C3
Ion
15:00 15:30 16:00 16:30 17:00 17:30 18:00 Time UT (HH:MM)
IMF
C3
Geotail + 10min
SuperDarn
12
MHD
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Cluster C3
Ion
15:00 15:30 16:00 16:30 17:00 17:30 18:00Time UT (HH:MM)
IMF
C3
Geotail + 10min
SuperDarn MHD
12
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OBSERVATIONS
• The dayside cusp region of the Earth‘s magnetosphere is known as a major source of ionospheric ions (e.g. Lockwood et al., 1985).
• The study of these ions provides information on energization processes (e.g. transverse ion heating by electrostatic, electromagnetic waves, parallel acceleration by DC electric fields)
•
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DMSP-F1516:12 UT
DMSP-F1517:52 UT
15:30
16:18
16:48
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Sketch of cusp motion
Bz<0, By<0
Cluster 3CuspCleft/LLBL
Bz>0, By<0
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ONOING STUDIES
Cusp:
Magnetopause
Tail
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Energy step structures of O+ and H+ ions in the cusp and polar cap,Ions transverse heating mechanisms
The heating can be associated
with broadband extra low frequency (BBELF) wave fields,waves near the lower hybrid (LH) frequency, or electromagnetic ion cyclotron (EMIC) waves near 0.5 fH+. The heating can also be correlated with auroral electrons, suprathermal electron burst (STEBs), or precipitating H+ ions. Furthermore, types 1 and 2 are often associated with field-aligned currents.